This invention concerns a cable connection through which two pieces of telecommunication equipment can send data to each other and receive data from each other and through which one piece of equipment can provide the other piece of equipment with the operating voltage it needs. The invention especially concerns a connection for connecting a unit located close to an antenna in a divided radio link and a unit located farther away with a cable connecting the units.
FIG. 1 is a simplified view of the main parts of a divided radio link. The radio link may be e.g. a microwave link. The main parts include an indoor Unit 2 which is located in the internal space of an equipment cabinet or such and wherein processing of the received Rx signal is performed. The signal has been received by an Outdoor Unit 5 located physically close to an antenna 1. It has received a radio frequency signal from the antenna and after frequency conversion it has sent it further over the cable to the indoor unit. The indoor unit 2 in the internal space correspondingly receives a signal from the network (not shown) and leads it to the unit""s transmission part Tx, which sends it further along a cable to the outdoor unit. This transmits it further to antenna 1.
Data transmission between both units takes place by way of a coaxial cable. The distance between the units, and thus the cable length, may vary from a few metres to a few hundred metres. The cable is connected to each unit by a Cable Interface CI, which adapts the data sent by the unit""s transmitter to the cable and correspondingly the data from the cable to the unit""s receiver.
Besides data, the cable must also transmit electric power from the indoor unit to the outdoor unit, if the latter is located in such a place, e.g. in a mast, where no own power source is available.
The problem is how in a divided radio link to transmit data and control in two directions, that is, in duplex form, and how to arrange the supply of electricity from one unit to another.
Three state-of-the-art basic solutions to the problem have been presented. According to the first solution, two separate coaxial cables are used, wherein in one cable useful data and control signals are transmitted from the indoor unit to the outdoor unit, while in the other cable the transmission is from the outdoor unit to the indoor unit. The core of one cable conducts the operating voltage from the indoor unit end as well as information transmitted by the indoor unit, while the core of the other coaxial cable conducts information received by the outdoor unit to the indoor unit.
According to another method, only one cable is used, whereby the transmission of data of either direction of transmission is modulated to some intermediate frequency.
According to a third method, one cable is also used, but signals in each direction are transmitted at different intermediate frequencies.
It is a drawback with the first method that an extra cable is needed, whereby corresponding cable adaptations are required. The method of implementation is costly. Since data is transmitted in both directions in separate cables, freedom from interference and non-existent cross-talk on the transmission path are advantages of this solution. Another advantage is the fact that baseband transmission of data is possible in both directions.
The drawback of the second method results from the circumstance that data is transmitted at an intermediate frequency in one direction. The cable interface hereby requires circuits performing up-conversion in the transmitter and down-conversion in the receiver. This entails a need for extra components on the boards, which again is a cost increasing factor. Of course, it is an advantage that only one cable is needed.
The drawback of the third method, as in the second method, is the need for extra components due to two different intermediate frequencies. Intermediate frequencies as such are available.
The present invention aims at a method and a device combining the good points of the known methods. Thus, the objective is an arrangement wherein the transmission requirement can be satisfied with just one cable and in such a way that baseband transmission of data and control signals is possible in both directions. Another objective is to transmit the supply electricity in the same cable as baseband signals.
The established objectives are achieved with the attributes presented in the independent claims.
According to the invention, the same wire of one cable is used both for transmitting data between an indoor unit and an outdoor unit as baseband transmission in full duplex form and for transmitting the operating voltage from the outdoor unit to the indoor unit. Any necessary arrangements are carried out in a cable interface CI.
The data to be transmitted which may be useful data or control data, is transmitted in the transmitter branch on the baseband through a hybrid connection to the cable, where it propagates to the unit of a distributed radio link at the other end. Correspondingly, the data which is sent by a unit at the other end arrives on the baseband on the same cable, is conducted to the said hybrid field; which separates the transmitted and received data and conducts the received data to the receiver branch. When the supply voltage is transmitted in the same cable with full duplex data, a diplexer is used between the hybrid connection and the cable end, whereby the common gate of the diplexer is connected to the cable, one gate to the voltage supply/reception point and one gate to the hybrid. Thus, the diplexer attends to separation by filtering of the supply voltage and the baseband data arriving from the cable. When using a diplexer, the analog data xe2x80x9cridesxe2x80x9d on top of the operating voltage in the cable to the reception end.
According to one embodiment, the hybrid field includes an inverter, which is used for forming inverted data from the data to be transmitted for echo elimination and for temporary storing and synchronising of the buffer""s inverted and non-inverted data, and a circuit having a point where data and inverted data are summed so that data to be transmitted will be seen in a variation of the potential of this point. This point is a virtual zero point forming one gate of the hybrid, and the data arriving from the cable can be read at this point.
In the receiver branch, the data received from the cable is processed in the desired manner. The processing depends on the line code of the data and it may be performed in an analog or digital manner and as a combination of these.